1. Field of the Invention
This invention relates to the field of high-energy laser amplifiers, and more particularly to pulse forming apparatus highly useful for laser radar, optical communication systems, and isotope separation purposes.
In these mentioned applications, laser pulses are required having appropriate temporal and spatial profiles. The pulse shaping technique to obtain these profiles must be widely variable and permit control of the output pulse shape over a large dynamic range.
The pulse forming apparatus of the present invention is highly advantageous in that the pulse shape is established at a very early stage, and this shape may be modified to compensate for distortion introduced by subsequent laser amplifiers. The present invention apparatus is further advantageous in that laser pulse shapes can be synthesized by methods consistent with the principles of Fourier analysis, so that once the temporal profile of the desired pulse is known, the individual spectral components can be determined from a Fourier analysis and the machine can then be adjusted to produce the required spectra. Importantly, these advantages of the invention apparatus are realized with a substantial reduction in the number of laser oscillators required to produce a pulse of given shape without loss of dynamic range and bandwidth.
2. Description of the Prior Art
High-energy CO.sub.2 laser amplifiers operate on vibrational bands having known center wavelengths commonly referred to as P(18), P(14), P(16), and so on. A vibrational band of great interest is the one having a center wavelength at about 10.6 .mu.m, (P(18)). High power can be obtained from a high-energy CO.sub.2 laser amplifier operating on this particular vibrational band. The rotational vibrational transition having a center wavelength at 10.6 .mu.m is also referred to as the 00.1 to 10.0 transition. Within a vibrational band, CO.sub.2 lasers can be tuned to operate on discrete rotational vibrational transitions or branches, e.g., P(14), P(16), P(18), P(20), and P(22).
The use of high-energy laser amplifiers may require a laser pulse source which produces predetermined pulse shapes over time, i.e., temporally shaped, replicative, i.e., coherent laser pulses having signal components on pre-selected rotational vibrational transitions with which to excite the high-energy laser amplifier. The power level of this laser amplifier pulse source is high, and that of the high-energy laser amplifier may be several orders of magnitude greater than that of the laser pulse source.
In the prior art, there is a fundamental problem in producing coherent pulses with an appropriate temporal profile. The problem is that distortion is introduced between the point of formation of the pulse and the target at which the pulse is used. To overcome the distortion, the laser pulse apparatus must provide a suitable level of flexibility in its operation, so that the output pulses can be temporally shaped over a suitable dynamic range to compensate for distortion. Some applications require pulse shapes having a very wide dynamic range, previously achievable only with large numbers of lasers. For example, to obtain a pulse having a dynamic range of 70 dB, the outputs of as many as 72 lasers heretofore would have had to be combined.
The need to use a large number of separate lasers to produce pulses having a large dynamic range is obviated by the present invention.